Process for sweetening petroleum cuts without regular addition of alkaline solution using a basic solid catalyst

ABSTRACT

A process for sweetening a petroleum cut containing mercaptans, wherein said petroleum cut is subjected to oxidation conditions by being contacted with a porous catalyst, in the presence of air said process being characterised in that said catalyst comprises 10 to 98% by weight of at least one mineral solid phase constituted of an alkaline aluminosilicate with a Si/Al atomic ratio less than or equal to 5, 1 to 60% by weight of active carbon, 0.02 to 2% by weight of at least one metal chelate and 0 to 20% by weight of at least one organic or mineral binding agent, has a basicity determined according to the 2896 ASTM standard with 20 milligrams of potash per gram and a total BET surface area of 10 m 2  g -1 , and contains inside its pore structure a permanent aqueous phase representing 0.1 to 40% by weight of dry catalyst.

This application is a continuation of application Ser. No. 08/105,998,filed Aug. 13, 1993, abandoned.

BACKGROUND OF THE INVENTION

The present invention is concerned with the sweetening, in a fixed bed,of petroleum cuts by catalytic oxidation into disulfides of themercaptans which they contain.

Theoretically, oxidation of this kind can be carried out easily bymixing the petroleum cut to be treated and an aqueous solution thereforan alkaline base, such as sodium, wherein a catalyst with a metalchelate base is added, in the presence of an oxidizing agent. Thepetroleum cut and the aqueous solution of the alkaline base are notmiscible. The successive stages in the transformation of the mercaptansinto disulfides is produced at the interface of the two liquid phases:

transformation of the mercaptans into mercaptides according to thereaction:

    RSH+B.sup.+ OH.sup.- →RS.sup.- B.sup.+ +H.sub.2 O

where B⁺ is the cation of the base under consideration (Na⁺ or K⁺, forexample),

oxidation of the mercaptides and their transformation into disulfidesaccording to the reaction:

    2R--S.sup.- B.sup.+ +H.sub.2 O+1/2O.sub.2 →R--S--S--R+2B.sup.+ OH

The capacity of the mercaptans to be oxidized and thus their ability tobe transformed into disulfides is dependent on their chemical structure.As a general rule, the greater the number of carbon atoms in thealiphatic chain of the mercaptan, the greater its reactivity.

In the case of petroleum cuts containing mercaptans which are difficultto oxidize, particularly if the content of these latter is high (somepetrol cuts and kerosene cuts, for example), it is preferable to treatthese petroleum cuts with a supported catalyst in the presence of analkaline base and of an oxidizing agent. A process of this kind is oftencalled a "sweetening process in fixed bed". The alkaline base which isusually used is most frequently sodium in aqueous solution; it isintroduced into the reaction medium either continuously orintermittently to maintain the alkaline conditions and the aqueousphase, both of which are necessary for the oxidation reaction. Theoxidizing agent which is usually air is mixed with the petroleum cut tobe sweetened. The metal chelate used as a catalyst is usually a metalphthalocyanine, such as cobalt phthalocyanine, for example. The reactionis usually carried out at a pressure of between 5 10⁵ and 30.10⁵Pascals, at a temperature of between 20° and 70° C. It is well known tothe skilled person that when the temperature is above about 70° C., thestability of the catalyst with a metal chelate base is rapidly reduced,causing degradation in the efficiency of the sweetening reaction.

Moreover, it is appropriate to renew the sodium solution which is usedup, firstly because of the impurities from the charge which aredissolved in the solution and which make it unsuitable for recycling,and secondly because of the variation in concentration of the base whichis reduced due to the water brought by the charge and due to thetransformation of the mercaptans into disulphides.

To overcome this problem, a proposal has been made (in particular in thepatents FR 2,343,043, U.S. Pat. No. 4,498,9078, and U.S. Pat. No.4,502,949) to suppress the use of aqueous sodium (or aqueous base).However, so that the reaction can take place in the usual way, theactive sites of the support must be placed in contact with themercaptans present in the petroleum charge, which presupposes ahomogeneous medium and thus the absence of an aqueous solution. However,apparently the molecules of water already present in the charge andparticularly those produced during the reaction promote the appearanceon the surface of the catalyst of an aqueous solution, which, if keptbeyond a certain threshold causes a reduction in catalytic activity. Aproposal has therefore been made either to incorporate a solid desiccantinto the support (U.S. Pat. No. 4,498,978), or to resorb this aqueousphase periodically by drying the catalyst using a polar solvent misciblein water, such as an alcohol (FR Patent 2,640,636). However, thesesolutions, despite being efficient, are inevitably quite expensive touse.

The prior art mentions a large number of supports which can be used tomake a catalyst capable of constituting a fixed bed, including:

active carbons obtained by pyrolysis of wood, peat, lignite, bone orvarious other carbonaceous materials;

clays and natural silicates, such as diatomaceous earth, fuller's earth,kieselguhr, attapulgite, feldspar, montmorillonite, halloysite andkaolin, and

natural or synthesized refractory mineral oxides, such as silica,zirconium oxide, thorium, boron or mixtures thereof.

Significant improvements enabling a partial or complete remedy to theaforementioned problems have been proposed in various patents, asfollows: EP 376,744, EP 252,853 and FR 2,651,791. These patents mentionthe use of solid catalysts constituted of a support containing:

60% to 90% by weight of a mineral matrix, 5 to 35% by weight ofpyrolysed carbon or active carbon, and 0.05 to 10% by weight of metalchelate. These catalysts can work with a water content of between 0.1and 50% by weight of the support, and they do not require an aqueousalkaline solution to be added continuously. The mineral part of thesupport can be selected from a group of constituents including aluminas,clays, aluminosilicates and silicates.

These latter catalysts, despite offering some progress compared withprior art catalysts are only really effective with charges which haverelatively low contents of mercaptans (<400 ppm approx.). They prove tobe ineffective with charges reputed as being difficult, and show a rapidfall (by a few days or a few dozen days) in activity. In view of suchunfavorable conditions, it can be necessary to continuously add smallamounts of alkaline aqueous solution which adversely affects the processemploying catalysts and which results in liquid rejection (sodiumsolution containing impurities, in particular) which produces the sameproblems as those already mentioned hereinabove.

SUMMARY OF THE INVENTION

In the present invention it has been discovered that this problem wasable to be avoided, even eliminated, by using a catalyst wherein thebasic matrix is obtained by incorporating an alkaline ion (Na⁺, K⁺) intoa mixed oxide structure which is essentially constituted of aluminiumoxides and silicon oxides combined.

Said aluminosilicates of alkaline metals, more particularly of sodiumand/or potassium, characterised by an Si/Al atomic ratio in theirstructure which is less than or equal to 5 (that is to say a SiO₂ /Al₂O₃ molar ratio which is less than or equal to 10) are clearly moreeffective than the other mineral compounds cited hereinabove. Thesealuminosilicates which are closely linked to the active carbon and to ametal chelate show optimum sweetening catalytic performances when thehydration level of the catalyst is between 0.1 and 40%, preferablybetween 1 and 25% by weight thereof.

In addition to their greater catalytic performance, these alkalinealuminosilicates are advantageous in that they are of very lowsolubility in aqueous medium, which allows prolonged use thereof in thehydrated state in treating the petroleum cuts to which a little water,or possibly aqueous alkaline solution, is added at regular intervals.This is not the case with mineral compounds of the alkaline silicate, oralkaline aluminate kind.

Thus, the sweetening process, in a fixed bed, of petroleum cutscontaining mercaptans according to the invention can be defined,generally speaking, as comprising contacting, under oxidationconditions, the petroleum cut to be treated with a porous catalystcomprising 10 to 98%, preferably 50 to 95% by weight, of at least onemineral solid phase constituted of an alkaline aluminosilicate with aSi/Al atomic ratio which is less than or equal to 5, preferably lessthan or equal to 3, 1 to 60% by weight of active carbon, 0.02 to 2% byweight of at least one metal chelate and 0 to 20% by weight of at leastone mineral or organic binding agent. This porous catalyst has abasicity determined in accordance with the 2896 ASTM standard of above20 milligrams of potash per gram and a total BET surface area of above10 m² g⁻¹, and inside its pore structure it contains a permanent aqueousphase representing 0.1 to 40%, preferably 1 to 25% by weight of the drycatalyst.

Of these basic mineral phases of the aluminosilicate type, mainly sodiumand/or potassium, which are particularly suitable, mention can be made,in particular, of a large number of phases (the majority of which aredescribed in the work by R. M. BARRER: Zeolites and Clay Minerals asSorbents and Molecular Sieves, Acad. Press. 1978):

when the alkali is mainly potassium;

kaliophilite: K₂ O, Al₂ O₃, a SiO₂ (1.8<a<2.4);

the feldspathoid called leucite: K₂ O, Al₂ O₃, a SiO₂ (3.5<a<4.5);

the zeolites of the type:

phillipsite: (K, Na)O, Al₂ O₃, a SiO₂ (3.0<a<5.0);

erionite or offretite: (K, Na, Mg, Ca)O, Al₂ O₃, a SiO₂ (4<a<8);

mazzite or Omega zeolite (W): (K, Na, Mg, Ca) O, Al₂ O₃, a SiO₂ (4<a<8);

L zeolite: (K, Na)O, Al₂ O₃, a SiO₂ (5<a<8).

when the alkali is sodium:

the amorphous sodium aluminosilicates, the crystalline organization ofwhich cannot be detected by X diffraction analysis, and the Si/Al atomicratio of which is less than or equal to 5, preferably less than or equalto 3;

sodalite: Na₂ O, Al₂ O₃, a SiO₂ (1.8<a<2.4);

As far as sodalite is concerned, various different types are knowncontaining ions or various alkaline salts trapped in the structure canbe prepared. These varieties are suitable for the present invention. Thefollowing are examples of ions or molecules which can be introduced intothe structure during synthesis: Cl⁻, Br⁻, ClO₃ ⁻, BrO₃.sup.═, 1O₃, NO₃,OH⁻, CO²⁻ ₃, SO₃ ²⁻, SO₃ ²⁻, CrO₄ ²⁻, MoO₄ ²⁻, PO₄ ³⁻, etc. in the formof alkaline salts, particularly sodium. The varieties which areparticularly preferable in the present invention are those containingthe OH⁻ ion in the form of NaOH and the S²⁻ ion in the form of Na₂ S.

-- nepheline: Na₂ O, Al₂ O₃, aSiO₂ (1.8<a<2.4);

-- tectosilicates of the following type:

sodalite,

analcime,

natrolite,

mesolite,

thomsonite,

clinoptilolite,

stilbite,

Na-P1 zeolite,

dachiardite,

chabasite,

gmelinite,

cancrinite,

faujasite comprising the synthetic zeolites X and Y,

A zeolite.

Preferably, said alkaline aluminosilicate is obtained by reacting inaqueous medium at least one clay (kaolinite, halloysite,montmorillonite, etc.) with at least one compound (hydroxide, carbonate,acetate, nitrate, etc.) of at least one alkaline metal, in particularsodium and/or potassium, this compound preferably being hydroxide,followed by a heat treatment at a temperature between 90° and 600° C.,preferably between 120° and 350° C.

Clay can also be treated thermally and crushed before being placed incontact with the alkaline solution. Thus, kaolinite and all the heattransformation products thereof (metakaolin, inverse spinel phase,mullite) can be used according to the process of the invention.

When the clay in question is kaolin, kaolinite and/or metakaolinconstitute the preferred base chemical reagents.

Like metal chelate, it is possible to deposit on the support any chelateused for this purpose in the prior art, particularly phthalocyanines,porphyrines or metal corrines. Particularly preferable are cobaltphthalocyanine and vanadium phthalocyanine. Use is preferably made ofmetal phthalocyanine in the form of a derivative, wherein there is aparticular preference for the sulphonates thereof availablecommercially, such as cobalt phthalocyanine mono- or disulphonate andmixtures of these.

The reaction conditions used in carrying out the process of theinvention differ mainly from the conditions known in prior art processesby the absence of aqueous base, higher temperature and faster spatialspeed per hour. Generally speaking, the conditions used are as follows:

-- temperature: 20° to 100° C.

-- pressure: 10⁵ to 30.10⁵ Pascal,

--amount of air oxidising agent: 1 to 3 kg/kg mercaptans,

--spatial speed per hour in v.v.h. (volume of charge per volume ofcatalyst and per hour): 1 to 10.

The water content of the catalyst used in the present invention can varyduring the operation in two different directions:

1) If the petroleum cut to be sweetened is dried beforehand, it can drawin gradually, by dissolving it, water which is present inside the porestructure of the catalyst. Under these conditions, the water contentdecreases regularly, and can thus decrease below the limit value of 0.1%by weight.

2) Inversely, if the petroleum cut to be sweetened is saturated withwater, and in view of the fact that the sweetening reaction isaccompanied by the production of one water molecule per molecule ofdisulphide formed, the water content of the catalyst can increase andattain values above 25% and in particular 40% by weight, at which valuesthe efficiency of the catalyst is impaired.

In the first instance, a sufficient amount of water can be added to thepetroleum cut upstream of the catalyst continuously or discontinuouslyto keep the hydration degree within the desired range.

In the second instance, it is sufficient to keep the temperature of thecharge fixed at a sufficient value, less than80° C., to solubilize thewater of the reaction resulting from transformation of the mercaptansinto disulphides. The temperature of the charge is thus selected in sucha way as to keep the water content of the support is kept between 0.1and 40% by weight of the support, preferably between 1 and 25% by weightthereof.

This range of preselected values for the water contents of the supportwill, of course, depend oh the very nature of the catalytic support usedduring the sweetening reaction. In fact, according to the patent FR2,651,791 if a number of catalytic supports are capable of being usedwithout aqueous sodium (or without an aqueous base), they will onlybecome active when their water content (also called hydration content ofsupport) is kept within a relatively restricted range of values whichcan vary depending on the supports, but which is seen to be associatedwith the silicate content of the support and structure of its pores.

It has also been observed during various tests that by adding a cationicsurfactant such as tetraalkylammonium hydroxide N(R)₄ OH to the chargeit is possible to significantly improve the efficiency of the catalystsof the present invention. Surfactants such as these are added to thecharge in the form of an aqueous solution containing between 0.01 and50% by weight, for example, and preferably 0.1 to 10% by weight ofsurfactant. In this case, the additions to the charge advantageouslyreplace the adding of water described hereinabove.

EXAMPLES

An embodiment of the invention will be described hereinafter in detail,as a non-limitative example:

In this embodiment, the reactor is supplied with the petroleum cut to besweetened in which the oxidizing agent which may be air is introduceddirectly. The petroleum cut treated is removed through a line whichsupplies a filter system intended to remove traces of water andincipient sulphur often produced during oxidation of the mercaptans andnot retained by the support. The treated charge is then transferredthrough to a storage chamber.

According to the invention, measuring probes which are placed upstreamand downstream of the reactor respectively permit a continuouscalculation of the water and mercaptans content to be made at the intakeand outlet of the reactor. It is thus possible to continuously checkwhether the water content of the catalytic support is increasing ordecreasing. Corrective measures can then be taken by modifying theamount of heat supplied to the charge by a heat exchanger placed overthe line upstream of the reactor.

The following examples illustrate the present invention without limitingthe scope thereof. Examples 3 and 4 describe the preparation ofcatalysts tested as comparisons.

EXAMPLE 1 Preparation of the Catalyst SX1

200 cm³ of an aqueous solution containing 130 g KOH is added to 272 gdry kaolin marketed by the FONJAC establishments, the degree of purityof which is approx. 83% (main impurities in % by weight: TiO₂ =0.2; Fe₂O₃ =0.9; CaO=0.15 K₂ O=1.5; Na₂ O=0.1; MgO=0.2; quartz=6.0;micas+feldspathoids=8.0).

The mixture is mixed for a few minutes at ambient temperature and isthen brought to 60° C. The liquid paste obtained is then mixed 30minutes at this temperature of 60° C.

87 g active carbon belonging to the company NORIT with a specificsurface area of approx 550 m² g⁻¹ are moistened with 77 cm³ of anaqueous solution containing 20 g KOH.

The active carbon thus moistened is added to the liquid kaolin pastewhich has been rendered alkaline previously, and they are mixed togetherfor about 30 minutes in a mixer with vanes, and then slightly heated (toabout 70° to 80° C.) to bring it to a plastic paste state which permitsshaping by extrusion.

The extrudates obtained which are 1.6 mm in diameter and which are cutinto lengths of between 3 and 10 mm are dried at 200° C. for 12 hours.The dried extrudates are very hard and very resistant to crushing. Xdiffraction structural analysis reveals that the structure of theinitial kaolinite is completely transformed at the temperature of 200°C. into kaliophilite of the composition K₂ O, Al₂ O₃, 2SiO₂.

The solid which is thus extruded is washed 3 times successively in 2liters of permuted water at ambient temperature for 30 minutes. It isthen immersed in 2 liters of a solution containing 1.0 g per liter ofsulphonated cobalt phthalocyanine of the type marketed by the Frenchcompany PROCATALYSE under the name "LCPS". All this is agitated atambient temperature for 30 hours; the solid is then filtered and washedonce in 1 liter of distilled water at ambient temperature.

This catalyst contains approximately 20% by weight carbon,

18.5% by weight potassium,

32.5% by weight silica,

and 4.9% by weight LCPS per kg of support.

Its surface area is 125 m² g⁻¹ and its basicity is above 80 mg. KOH perg.

This catalyst is then dried slowly at 50° C. in a stove until it has aresidual water content of 6% by weight. This catalyst is called SX1.

EXAMPLE 2 Preparation of the SX2 Catalyst

First of all, a liquid paste is prepared, as described in Example 1,which is constituted of 187 g dry kaolin and 135 cm³ of a solutioncontaining 90 g KOH potash. This paste is mixed at 60° C. for 15minutes.

60 cm³ of a solution containing 33 g of silica in the form of commercialpotassium orthosilicate is added to 87 g active carbon. 40 cm³ of asolution containing 28 g alumina in the form of aluminium nitrate isthen added. This mixture is mixed at 50° C. for 30 minutes. 40 cm³ of asolution is then added containing 30 g KOH. All this is then mixed forabout 30 minutes.

The kaolin paste which is rendered alkaline is then mixed with thecombination of active carbon and amorphous potassium silicoaluminate.All this is mixed for 15 minutes, and is then slightly heated to bringit to a plastic paste state permitting easy extrusion.

The support in the form of extrudates thus obtained is then subjected tothe same treatments as in Example 1.

The catalyst resulting from these treatments contains approx.:

20% by weight carbon,

14.5% by weight potassium,

and 4.8 g LPCS per kg of support.

Its surface area is 131 m² g⁻¹ and its basicity is greater than 60 mg.KOH per g.

X diffraction structural analysis of the catalyst obtained reveals thathere too the mineral part is essentially constituted of kaliophilite.

The catalyst is then dried slowly at 50° C. in a stove until it reachesa residual water content of 8% by weight. This catalyst is called theSX2 catalyst.

EXAMPLE 3 Preparation of the SX3 Catalyst

200 cm³ of an aqueous solution containing 102 g NaOH is added to 272 gdry kaolin marketed by the FONJAC establishments, the degree of purityof the dry kaolin being about 83% (main impurities in % by weight: TiO₂=0.2; Fe₂ O₃ =0.9; CaO=0.15; K₂ O=1.5; Na₂ O=0.1; MgO=0.2; quartz=6.0;micas+feldspathoids=8.0).

The mixture is mixed for a few minutes at ambient temperature and isthen brought to 60° C. The liquid paste which is obtained is then mixedfor 30 minutes at this temperature of 60° C.

87 g active carbon of the company NORIT with a specific surface area ofapprox. 550 m² g⁻¹ is moistened with 77 cm³ of an aqueous solutioncontaining 17 g NaOH.

The active carbon moistened thus is added to the liquid paste of kaolinewhich has been rendered alkaline beforehand and all of this is mixed forabout 30 minutes in a mixer with vanes and is then slightly heated (toabout 70° to 80° C.) to bring it to a plastic paste state permittingshaping by extrusion.

The extrudates obtained are 1.6 mm in diameter and are cut into lengthsof between 3 and 10 mm, and dried at 200° C. for 12 hours. The driedextrudates are very hard and very resistant to crushing. X diffractionstructural analysis reveals that the structure of the initial kaolin iscompletely transformed at the temperature of 200° C. into a compound ofthe sodalite type of composition Na₂ O, Al₂ O₃, 2SiO₂.

The solid which is thus extruded is washed 3 times successively in 2liters permuted water, at ambient temperature for 30 minutes. It is thenimmersed in 2 liters of a solution containing 1.0 g per liter ofsulphonated cobalt phthalocyanine of the type marketed by the Frenchcompany PROCATALYSE under the name "LCPS".

All these are agitated at ambient temperature for 30 hours; the solid isthen filtered and washed once in 1 liter distilled water at ambienttemperature.

This catalyst contains approx.

20% by weight carbon

9% by weight sodium

32.5% by weight silica,

and 4.9 g LCPS per kg of support

Its surface area is 125 m² g⁻¹ and its basicity is greater than 100 mg.KOH per g.

The catalyst is then dried slowly at 50° C. in a stove until it Peachesa residual water content of less than 7% by weight. This catalyst iscalled SX3.

EXAMPLE 4 Preparation of the SX4 Catalyst

100 g active carbon are wetted with 88 cm³ of an aqueous solution. 400 galumina Al₂ O₃ in the form of powder pseudoboehmite and marketed underthe name of "gel Condea SB3" by the company CONDEA is acidified with 580cm³ of a solution containing 28 g pure nitric acid.

The moistened active carbon is added to the acidified alumina, and ismixed for 30 minutes until a homogeneous paste is obtained. The productis then dried at 70°-80° C. for a few minutes, with it being mixed toobtain a thick extrudable paste. After extrusion, the product is driedat 200° C. in air for 12 hours and then calcined at 500° C. in nitrogenfor 2 hours.

The support, thus obtained, in the form of extrudates is then subjectedto the same treatments as in Examples 1 and 2.

The catalyst resulting from these treatments contains about:

20% by weight carbon,

and 3.8 g LCPS per kg of support.

Its surface area is 282 m² g⁻¹ and its basicity is 10 mg. KOH per g.

It is dried slowly at 50° C. in a stove until it reaches a residualwater content of 6% by weight. It will be called SX4 hereinafter.

EXAMPLE 5 Preparation of Catalyst SX5

100 g active carbon are moistened with 88 cm³ of an aqueous solutioncontaining 10 g KOH.

400 g alumina Al₂ O₃ in the form of powder pseudoboehmite marketed underthe name of "gel Condea SB3" by the company CONDEA is acidified with 540cm³ of a solution containing 28 g pure nitric acid.

The moistened active carbon which has been rendered alkaline is added tothe acidified alumina and the mixture is mixed for 30 minutes to obtaina homogeneous paste. 40 cm³ of a solution containing 10 g KOH is thenadded slowly by mixing. It is mixed for another 30 minutes, and thendried at 70°-80° C. until a thick extrudable paste is obtained. Afterextrusion, the solid is dried at 200° C. in nitrogen for 2 hours.

The support thus obtained, in the form of extrudates, is then subjectedto the same treatments as those in Examples 1, 2 and 3.

The catalyst resulting from these treatments contains approximately:

20% by weight carbon

2.6% by weight potassium

and 5.1 g LCPS per kg of support.

Its surface area is 244 m² g⁻¹ and its basicity is 16 mg. KOH per g.

The catalyst is then dried slowly at 50° C. in a stove until it reachesa residual water content of 6% by weight. It is called SX5 hereinafter.

EXAMPLE 6 Evaluation and Comparison of the Properties of the SX1, SX2,SX3, SX4 and SX5 Catalysts in a Test for Sweetening Petroleum Cuts

The charge used for the sweetening test is a kerosene obtained from acrude Iranian light. The properties of the kerosene are given in Table 1hereinafter:

                  TABLE 1                                                         ______________________________________                                        PROPERTIES OF THE KEROSENE TO BE SWEETENED                                    R--SH (ppm)           1.67                                                    TAN (mg KOH/g)        0.050                                                   SAYBOLT COLOUR        25                                                      TOTAL SULPHUR % by weight                                                                           0.285                                                   INITIAL POINT °C.                                                                            151                                                     FINAL POINT °C.                                                                              243                                                     VOLUMETRIC MASS g/l   0.8                                                     WATER CONTENT (ppm)   150                                                     PHENOLS (ppm)         610                                                     THIOPHENOLS (ppm)     <10                                                     ______________________________________                                    

The 5 catalysts are evaluated and compared on this charge under thefollowing operating conditions:

-- Temperature=40° C.

-- Pressure=0.7 MPa (7 bars) relative

-- VVH=variable from 1 to 7 (hour)⁻¹

-- flow of air=variable from 1 to 1.2 times the stoichiometry of thereaction.

-- addition of water to the charge at a rate of 1 cm³ per kg of charge.

The results obtained under these conditions over several dozen orhundreds of hours testing depending on the case at hand with the SX1,SX2, SX3, SX4 and SX5 catalysts are shown in Tables 2, 3, 4, 6 and 7respectively.

Table 5 shows the performance of the SX3 catalyst, all other conditionsbeing the same, when, after 2000 hours of testing, the adding of wateris replaced by the adding of an aqueous solution containing 2% by weightof ammonium tetrabutyl hydroxide N(Bu)₄ OH.

                                      TABLE 2                                     __________________________________________________________________________    RESULTS OBTAINED WITH THE CATALYST SX1                                        TIME TEMP                                                                              PRESSURE     VVH   R--SH                                                                              DOCTOR                                       (hour)                                                                             (°C.)                                                                      (Bars rel)                                                                           STOICH.                                                                             (hour - 1)                                                                          (ppm)                                                                              Test                                         __________________________________________________________________________     0   40  7      1.2   1                                                        13  40  7      1.2   1     5.5  negative                                      37  40  7      1.2   1     0.5  negative                                      45  passage with VVH = 1.7      negative                                      61  40  7      1.2   1.7   0.5  negative                                      85  40  7      1.2   1.7   0.9  negative                                     109  40  7      1.2   1.7   0.9  negative                                     133  40  7      1.2   1.7   0.6  negative                                     135  Passage with VVH = 1.7 & stoichiometry = 1.1                                                              negative                                     159  40  7      1.1   1.7   1.6  negative                                     183  40  7      1.1   1.7   1.7  negative                                     184  Passage with stoichiometry = 1                                                                            negative                                     207  40  7      1.0   1.7   0.8  negative                                     231  40  7      1.0   1.7   1    negative                                     251  40  7      1.0   1.7   1.4  negative                                     275  40  7      1.0   1.7   1.8  negative                                     299  40  7      1.0   1.7   0.4  negative                                     323  40  7      1.0   1.7   1.5  negative                                     347  40  7      1.0   1.7   1.2  negative                                     371  40  7      1.0   1.7   1.1  negative                                     __________________________________________________________________________

                  TABLE 3                                                         ______________________________________                                        RESULTS OBTAINED WITH THE CATALYST SX2                                                      PRES-                                                                         SURE            VVH         DOC-                                TIME  TEMP    (Bars           (hour R--SH TOR                                 (hours)                                                                             (°C.)                                                                          rel)    STOICH. -1)   (ppm) Test                                ______________________________________                                         0    40      7       1.0     1.7                                              15   40      7       1.0     1.7   1.1   negative                             38   40      7       1.0     1.7   3.1   negative                             50   40      7       1.0     1.7   0.5   negative                             62   40      7       1.0     1.7   0.7   negative                            110   40      7       1.0     1.7   0.9   negative                            130   40      7       1.0     1.7   0.9   negative                            155   40      7       1.0     1.7   1.0   negative                            182   40      7       1.0     1.7   0.8   negative                            207   40      7       1.0     1.7   1.2   negative                            230   40      7       1.0     1.7   1.1   negative                            243   40      7       1.0     1.7   0.8   negative                            265   40      7       1.0     1.7   0.9   negative                            275   40      7       1.0     1.7   0.9   negative                            310   40      7       1.0     i.7   1.0   negative                            320   40      7       1.0     1.7   1.2   negative                            380   40      7       1.0     1.7   1.2   negative                            ______________________________________                                    

                  TABLE 4                                                         ______________________________________                                        RESULTS OBTAINED WITH THE CATALYST SX3                                                      PRES-                                                                         SURE            VVH         DOC-                                TIME  TEMP    (Bars           (hour R--SH TOR                                 (hours)                                                                             (°C.)                                                                          rel)    STOICH. -1)   (ppm) Test                                ______________________________________                                         0    40      7       1.0     1.7                                              15   40      7       1.0     1.7   1.1   negative                             35   40      7       1.0     1.7   2.2   negative                             45   40      7       1.0     1.7   0.7   negative                            108   40      7       1.0     1.7   1.0   negative                            152   40      7       1.0     1.7   1.0   negative                            210   40      7       1.0     1.7   1.2   negative                            258   40      7       1.0     1.7   1.1   negative                            315   40      7       1,0     1.7   1.0   negative                            410   40      7       1.0     1.7   1.5   negative                            492   40      7       1.0     1.7   1.8   negative                            507   40      7       1.0     1.7   1.7   negative                            600   40      7       1.0     1.7   1.8   negative                            705   40      7       1.0     1.7   2.1   negative                            812   40      7       1.0     1.7   2.4   negative                            904   40      7       1.0     1.7   2.8   negative                            1020  40      7       1.0     1.7   3.9   negative                            1950  40      7       1.0     1.7   7.3   positive                            ______________________________________                                    

                                      TABLE 5                                     __________________________________________________________________________    RESULTS OBTAINED WITH                                                         THE CATALYST SX3 WITH THE ADDITION OF A                                       CATIONIC SURFACE-ACTIVE AGENT,                                                AMMONIUM TETRABUTYL HYDROXIDE (N(Bu).sub.4 OH).                               Time                                                                              Temperature                                                                            Pressure WH    R--SH                                                                             Doctor                                        (hours)                                                                           (°C.)                                                                           Bars rel.                                                                          Stoich.                                                                           (hour -1)                                                                           ppm test                                          __________________________________________________________________________    1020                                                                              40       7    1.0 1.7   3.9 negative                                      1950                                                                              40       7    1.0 1.7   7.3 positive                                      2000                                                                              40       7    1.0 1.7   7.5 positive                                      2001                                                                              Addition of                                                                   N(Bu).sub.4 OH                                                            2050                                                                              40       7    1.0 1.7   3.1 negative                                      2106                                                                              40       7    1.0 1.7   2.4 negative                                      2203                                                                              40       7    1.0 1.7   2.5 negative                                      2298                                                                              40       7    1.0 1.7   2.7 negative                                      2415                                                                              40       7    1.0 1.7   3.2 negative                                      2620                                                                              40       7    1.0 1.7   3.3 negative                                      2625                                                                              Stop addition                                                                 N(Bu).sub.4 OH                                                            2702                                                                              40       7    1.0 1.7   3.4 negative                                      2807                                                                              40       7    1.0 1.7   3.4 negative                                      2918                                                                              40       7    1.0 1.7   3.7 negative                                      3005                                                                              40       7    1.0 1.7   4.0 negative                                      __________________________________________________________________________

                  TABLE 6                                                         ______________________________________                                        RESULTS OBTAINED WITH THE CATALYST SX4                                                      PRES-                                                                         SURE            VVH         DOC-                                TIME  TEMP    (Bars           (hour R--SH TOR                                 (hours)                                                                             (°C.)                                                                          rel)    STOICH. -1)   (ppm) Test                                ______________________________________                                         0    40      7       1.0     1.7   --    --                                  10    40      7       1.1     1.7    6.5  positive                            20    40      7       1.2     1.0   10.0  positive                            40    40      7       1.2     1.0   18.1  positive                            55    40      7       1.2     1.0   30.5  positive                            80    40      7       1.2     1.0   45.5  positive                            95    40      7       1.2     1.0   62.0  positive                            ______________________________________                                    

                  TABLE 7                                                         ______________________________________                                        RESULTS OBTAINED WITH THE CATALYST SX5                                                      PRES-                                                                         SURE            VVH         DOC-                                TIME  TEMP    (Bars           (hour R · SH                                                                     TOR                                 (hours)                                                                             (°C.)                                                                          rel)    STOICH. -1)   (ppm) Test                                ______________________________________                                         0    40      7       1.0     1.7                                             13    40      7       1.0     1.7   2.2   negative                            25    40      7       1.0     1.7   4.1   negative                            42    40      7       1.1     1.0   5.5   positive                            50    40      7       1.2     1.0   9.5   positive                            82    40      7       1.2     1.0   14.1  positive                            105   40      7       1.2     1.0   20.8  positive                            ______________________________________                                    

In the light of these results, it is clear that the SX1, SX2, and SX3catalysts according to the present invention have sweetening propertiesfor the kerosene charge which is used here which are clearly superior tothose of the SX4 and SX5 catalysts. In particular, there is a noticeableimprovement in their performance in converting the mercaptans intodisulphides and the stability of their efficiency over the course oftime.

We claim:
 1. A process for sweetening a petroleum cut containingmercaptans comprising subjecting said petroleum cut to oxidationconditions by contacting the cut with a porous catalyst in the presenceof air, wherein said catalyst comprises 10 to 98% by weight of at leastone solid mineral phase which is an alkaline zeolite or tectosilicatewith a Si/Al atomic ratio which is less than or equal to 5, 1 to 60% byweight active carbon, 0.02 to 2% by weight of at least one metal chelateand 0 to 20% by weight of at least one mineral or organic binding agent,said catalyst having a basicity determined according to ASTM standard2896 which is above 70 mg of potash per gram, a total BET surface areawhich is greater than 10 m² g⁻¹, and inside its pore structure ahydration rate which is 0.1 to 40% by weight of dry catalyst.
 2. Aprocess according to claim 1, wherein the Si/Al ratio of the alkalinezeolite or tetosilicate is less than or equal to
 3. 3. A processaccording to claim 1, wherein the alkaline zeolite or tectosilicate is asodium or a potassium zeolite or tectosilicate.
 4. A process accordingto claim 3, wherein the sodium zeolite or tectosilicate is a sodalitecompound of the approximate formula Na₂ O, Al₂ O₃, a SiO₂, with a valueof 1.8 to 2.4.
 5. A process according to claim 3, wherein the sodium orpotassium zeolite or tectosilicate is obtained by reacting in aqueousmedium at least one clay with at least one of sodium hydroxide orpotassium hydroxide, followed by a heat treatment at a temperature ofbetween 90° and 600° C.
 6. A process according to claim 5, wherein theclay is activated thermally beforehand, and then crushed before it isplaced in contact with the sodium hydroxide or potassium hydroxide inaqueous media.
 7. A process according to claim 3, wherein the alkalinezeolite or tectosilicate is at least partially a zeolite, the major partof which, at least, contains sodium.
 8. A process according to claim 1,wherein the alkaline zeolite or tectosilicate represents 50 to 95% byweight of sweetening catalyst, calculated in relation to the weight ofdry catalyst.
 9. A process according to claim 1, wherein the metalchelate contained in the catalyst is a cobalt phthalocyanine.
 10. Aprocess according to claim 1, wherein the hydration rate is between 1and 25% by weight relative to the dry catalyst.
 11. A process accordingto claim 1, wherein the temperature is between 20° and 100° C., thepressure 10⁵ to 30.10⁵ Pa, the proportion of air is from 1 to 3 kg/kg ofmercaptans and the hourly space velocity is 1 to 10 v.v.h.
 12. A processaccording to claim 1, wherein an anionic or cationic surface-activeagent is added in the form of an aqueous solution continuously ordiscontinuously to the charge which is to be sweetened.
 13. A processaccording to claim 1, wherein the surface-active agent is a cationicagent.
 14. A process according to claim 1, wherein the temperature isselected in such a way as to maintain the water content of the supportwithin the desired range.
 15. A process according to claim 1, whereinthe petroleum cut treated is a petrol or a kerosene.
 16. A processaccording to claim 13, wherein the surface-active agent is a quaternaryammonium hydroxide salt.
 17. A process according to claim 1, whereinwater is added continuously or discontinuously to the process so as tomaintain the catalyst within the hydration rate.
 18. A process accordingto claim 10, wherein water is added continuously or discontinuously tothe process so as to maintain the catalyst within the hydration rate.19. A process for sweetening a petroleum cut containing mercaptanscomprising subjecting said petroleum cut to oxidation conditions bycontacting the cut with a porous catalyst in the presence of air,wherein said catalyst comprises 10 to 98% by weight of at least onesolid mineral phase which is an alkaline zeolite or tectosilicate with aSi/Al atomic ratio which is less than or equal to 5, 1 to 60% by weightactive carbon, 0.02 to 2% by weight of at least one metal chelate and 0to 20% by weight of at least one mineral or organic binding agent, saidcatalyst having a basicity determined according to ASTM standard 2896which is above 100 mg of potash per gram, a total BET surface area whichis greater than 10 m² g⁻¹, and inside its pore structure a hydrationrate of 0.1 to 40% by weight of dry catalyst.
 20. A process according toclaim 19, wherein the hydration rate is between 1 and 25% by weightrelative to the dry catalyst.
 21. A process according to claim 1,wherein the basicity of the catalyst is greater than 80 mg of potash pergram.
 22. A process according to claim 1, wherein the hydration rate is10 to 40% by weight.
 23. A process according to claim 1, wherein thehydration rate is 20 to 40% by weight.
 24. A process according to claim1, wherein the hydration rate is 25 to 40% by weight.
 25. A process forsweetening a petroleum cut containing mercaptans comprising subjectingsaid petroleum cut to oxidation conditions by contacting the cut with aporous catalyst in the presence of air, wherein said catalyst ishomogenous and comprises, closely linked together, 10 to 98% by weightof at least one solid mineral phase which is an alkaline zeolite ortectosilicate with a Si/Al atomic ratio which is less than or equal to5, 1 to 60% by weight active carbon, 0.02 to 2% by weight of at leastone metal chelate and 0 to 20% by weight of at least one mineral ororganic binding agent, said catalyst having a basicity determinedaccording to ASTM standard 2896 which is above 70 mg of potash per gram,a total BET surface area which is greater than 10 m² g⁻¹, and inside itspore structure a hydration rate which is 0.1 to 40% by weight of drycatalyst.